Abstract: Kunteyi depression of Qaidam Basin features in deeply buried oil reservoir and complex geologic structure.To realize safe,optimum and fast drilling in this high risk formation,plugging and film forming drilling fluid is developed on the theories of ideal packing,filming forming,and ultra-low permeability drilling fluid.Experiments of submerging depth of sand bed,sealing properties of membrane structure,pressure and filtration,and permeability recovery are conducted to test the properties of the drilling fluid.In addition,drilling fluid formulation is selected in accordance with the porosity,permeability,lithology,bottomhole temperature,drilling procedure of Kun-2 well.Application shows that this kind of drilling fluid has excellent wellbore stability and enables Kunteyi formation to realize no accidents,increase drilling speed,shorten drilling cycle,and successfully complete drilling tasks.